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A nest is a structure built by certain animals to hold its eggs, its offspring, or occasionally the animal itself. Although nests are most closely associated with birds, members of all classes of vertebrates and some invertebrates construct nests. They may be composed of organic material such as twigs, grass, and leaves, or may be a simple depression in the ground, or a hole in a rock, tree, or building. Human-made materials, such as string, plastic, cloth, or paper, may also be used. Nests can be found in all types of habitat. Nest building is driven by a biological urge known as the nesting instinct in birds and mammals. Generally each species has a distinctive style of nest. Nest complexity is roughly correlated with the level of parental care by adults. Nest building is considered a key adaptive advantage among birds, and they exhibit the most variation in their nests ranging from simple holes in the ground to elaborate communal nests hosting hundreds of individuals. Nests of prairie dogs and several social insects can host millions of individuals. ==Nest building== Nest building is often driven by a biological urge in pregnant animals to protect one's offspring known as the nesting instinct. Animals build nests to protect their eggs, their offspring, or themselves from danger. The simplest nests are designed to hide eggs from predators, shield them from the sun or other environmental factors, or simply keep them from being scattered in ocean currents. In some cases, nests also help provide safety in numbers for egg-laying animals. Many nest builders provide parental care to their young, while others simply lay their eggs and leave. Brooding (incubating eggs by sitting on them) is common among birds. In general, nest complexity increases in relation to the level of parental care provided.〔 Nest building reinforces social behavior, allowing for larger populations in small spaces to the point of increasing the carrying capacity of an environment. Insects that exhibit the most complex nest building also exhibit the greatest social structure. Among mammals, the naked mole-rat displays a caste structure similar to the social insects while building extensive burrows that house hundreds of individuals.〔 At the most basic level, there are only two types of nest building: sculpting and assembly. Sculpting is the process of removing material to achieve a desired outcome. Most commonly this entails burrowing into the ground or plant matter to create a nesting site. Assembly entails gathering, transporting, and arranging materials to create a novel structure. Transportation has the greatest time and energy cost so animals are usually adapted to build with materials available in their immediate environment. Versatility in use of construction material may be an adaptive advantage (less energy used to gather materials) or a disadvantage (less ability to specialize construction). The available evidence suggests that natural selection more often favors specialization over flexibility in nest construction.〔 Plant matter is the most common construction material for nests. Other common materials include fur or feathers, perhaps from the animal itself, mud or dirt, fecal matter, and specialized secretions from the animal's body. Nest building can have a substantial impact on the environment in which animals live. The combined digging activity of termites and mole-rats in South Africa has created a "mima prairie" landscape marked by huge areas of flat land punctuated by mounds wide and high. Similar structures exist in the United States (created by pocket gophers) and Argentina (rodents of the ''Ctenomys'' genus). Nests constructed by megapode birds have been mistaken for anthropological features by professionals, due to their exceptional height () and abundance (hundreds in a single location).〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「nest」の詳細全文を読む スポンサード リンク
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